U.S. Pat. Nos. 5,297,617 and 5,445,215, both entitled FAN WITH HEAT SINK, and owned by the same entity as this patent application, teach that the area surrounding the fan blade tips in an axial flow fan has high velocity, very turbulent air, and that the periphery of an axial flow fan is an excellent heat sink, particularly if the inside of the fan duct and/or the fan blade are modified as taught therein to enhance the heat sinking. These are modified axial flow fans, and the air flow through them may be partly or completely redirected to fins or other features in the periphery of the fan duct, to remove heat therefrom. These patents are incorporated herein by reference.
Other related patent applications are: a provisional patent application entitled FAN WITH HEAT SINK USING STAMPED HEAT SINK FINS, Ser. No. 60/062,171, filed 16 Oct. 1997; a utility patent application of the same name, Ser. No. 09/174,374, filed 15 Oct., 1998 and issued as U.S. Pat. No. 6,125,920 on 3 Oct., 2000; a utility patent application of the same name, Ser. No. 09/678,424 filed 2 Oct., 2000; a utility patent application of the same name, Ser. No. 10/064,071 filed Jun. 6, 2002, and a utility patent application entitled FAN WITH HEAT SINK, Ser. No. 10/064,060 filed Jun. 5, 2002.
It is well known that a plurality of closely spaced fins makes an excellent heat sink. However, there is a boundary layer that is a very persistent viscous layer of air on the surfaces of the heat sink fins, requiring very high velocity and turbulent air flow to dissipate the boundary layer for heat flow into the air. In prior art heat sinks, this required very large, powerful and noisy fans.
Heat sinks made with a plurality of closely spaced fins are sometimes made by bonding heat sink fins into a grooved plate. A separate fan may blow air over the fins.
In the patent applications referenced above, air is not blown through the fins, as in going in one surface and out another, but rather, air is agitated between the fins on a single surface with no separate exit air path. The air in the vicinity of a plurality of fan blades is very turbulent and has a oscillating component as each of the fan blades passes any point on fins. Air is thus scrubbed in and out of the fins with very high local velocities to break up the boundary layer and transfer heat to the air. These fins can be on an inner surface, with internal fan blades, or on an external surface with external fan blades or both, or on a circular array of buttresses or posts rising from a plate. In the latter, there may be some air flow through the fins as well, but this is incidental. High velocity and turbulent air is needed to break up the boundary layer, but a modest movement of air is sufficient to transport the heat away. The rotation of the fan blades causes enough incidental air motion around the fan with heat sink to accomplish this. Thus a fan of low or moderate power can cause more vigorous local air movement immediately on the heat sink fins if the fan blades are very close than even a very powerful fan that is spaced apart. The fans and heat sinks of these inventions will be smaller, lighter, much quieter and consume much less power than prior art fans and heat sinks of the same heat capacity.
One embodiment of the invention teaches that a fan and heat sink can be a cold plate, which could be used for brick power supply modules, computer processors and the like or any other application requiring the removal of heat.
The heat sink fins may comprise a flat coil spring like strip of metal, similar to the familiar “Slinky” toy, placed in or on a cylinder of metal, or it may be like a closely pitched “clock spring” bonded onto a plate. Alternatively, the heat sink fins may comprise a stack of stamped metal rings pressed on or in a cylinder of metal. Alternatively, the heat sink fins may comprise a formed strip of metal that has been wrapped around a metal cylinder or attached to a flat plate. These may rest on the surface or may be pressed into complementary grooves in the surface.